Firefox 3.1 Beta 2 two biggest things that jump out right off the bar is the addition of private browsing and the new Trace Monkey JavaScript engine.

Trace Monkey is available in Firefox 3 but has to be enabled, now with 3.1 it is on by default. The time it takes to render pages with 3.1 is a considerably boost from previous Firefox versions.

Of course, this is a beta version so there are a few bugs, such as a few of my favorite sites don’t quite render correctly. I am sure this will be fixed for in final version. The beta version scores a 92/100 in the Acid 3 test.

The Private browsing mode is a feature a lot of people wanted for awhile and Firefox has listened. Firefox will not record browsing, search, download, web form history, cookies and temporary Internet files while using the Private browsing mode. Since Firefox 3.1 Beta 2 is still, well beta, most likely you current add ons and themes will not work if you choose to download it. Be warned that if you download and try the new beta version and delete your previous version of Firefox, then you will lose all your add on and theme data.

For those of you who do not want to download the beta version but want to enable Trace Monkey in Firefox 3 follow these steps:
1. Type about:config in the address bar and press enter
2. Click “I will be careful”
3. Scroll down and find javascript.options.jit.chrome.
4. Double click and change the setting from false to true.